A. Field of the Invention
This invention relates to the field of computerized techniques for orthodontic treatment planning for human patients. More particularly, the invention is directed to measuring tooth displacements in a consistent and accurate manner during virtual orthodontic treatment planning using a novel orthodontic reference coordinate system in conjunction with a tooth axes system. The invention is also directed to moving the teeth from initial positions to desired positions in an accurate, consistent and reproducible manner.
B. Description of Related Art
The traditional process of diagnosis and treatment planning for a patient with orthodontic problems or disease typically consists of the practitioner obtaining clinical history, medical history, dental history, and orthodontic history of the patient supplemented by 2D photographs, 2D radiographic images, CT scans, 2D and 3D scanned images, ultrasonic scanned images, and in general non-invasive and sometimes invasive images, plus video, audio, and a variety of communication records. Additionally, physical models, such as made from plaster of paris, of the patient's teeth are created from the impressions taken of the patient's upper and lower jaws. Such models are manually converted into teeth drawings by projecting teeth on drawing paper. Thus, there is a large volume of images and data involved in the diagnosis and treatment planning process. Furthermore, the information may require conversion from one form to another and selective reduction before it could become useful. There are some computerized tools available to aid the practitioner in these data conversion and reduction steps, for example to convert cephalometric x-rays (i.e., 2 dimensional x-ray photographs showing a lateral view of the head and jaws, including teeth) into points of interest with respect to soft tissue, hard tissue, etc., but they are limited in their functionalities and scope. Even then, there is a fairly substantial amount of manual work involved in these steps.
Orthodontists routinely prescribe translational displacements and rotational movements of teeth of orthodontic patients during treatment planning. The translational displacements include mesial or distal (miseodistal), buccal or lingual (buccolingual), and coronal or gingival displacements. The rotational movements include torque, angulation and rotation. Generally, the translation displacements are specified in mm; and the torque, angulation and rotation movements in gradient or degrees. Additionally, measurements of tooth positions in terms of these translational displacements and rotational movements are used in assessing the treatment needs. Often, a physical model of the dentition of a patient is created and used by the practitioner in manually measuring the tooth positions and assessing the required teeth displacements and movements. The measurements are basically done in two-dimensions and are time consuming, prone to inherent inaccuracies; and lack consistency and reproducibility.
Consequently, the practitioner is left to mental visualization, and chance process to select the treatment course that would supposedly work. Furthermore, the diagnosis process is some-what ad-hoc and the effectiveness of the treatment depends heavily upon the practitioner's level of experience. Often, due to the complexities of the detailed steps and the time consuming nature of them, some practitioners take a shortcut, relying predominantly on their intuition to select a treatment plan. For example, the diagnosis and treatment planning is often done by the practitioner on a sheet of acetate placed over the X-rays. All of these factors frequently contribute towards trial and error, hit-and-miss, lengthy and inefficient treatment plans that require numerous mid-course adjustments. While at the beginning of treatment things generally run well as all teeth start to move at least into the right direction, at the end of treatment a lot of time is lost by adaptations and corrections required due to the fact that the end result has not been properly planned at any point of time. By and large, this approach lacks reliability, reproducibility and precision. More over, there is no comprehensive way available to a practitioner to stage and simulate the treatment process in advance of the actual implementation to avoid the often hidden pitfalls. And the patient has no choice and does not know that treatment time could be significantly reduced if proper planning was done.
In recent years, computer-based approaches have been proposed for aiding orthodontists in their practice. However, these approaches are limited to diagnosis and treatment planning of craniofacial structures, including the straightening of teeth. See Andreiko, U.S. Pat. No. 6,015,289; Snow, U.S. Pat. No. 6,068,482; Kopelmann et al., U.S. Pat. No. 6,099,314; Doyle, et al., U.S. Pat. No. 5,879,158; Wu et al., U.S. Pat. No. 5,338,198, and Chisti et al., U.S. Pat. Nos. 5,975,893 and 6,227,850, the contents of each of which is incorporated by reference herein. Also see imaging and diagnostic software and other related products marketed by Dolphin Imaging, 6641 Independence Avenue, Canoga Park, Calif. 91303-2944.
A method for generation of a 3D model of the dentition from an in-vivo scan of the patient, and interactive computer-based treatment planning for orthodontic patients, is described in U. U.S. Pat. No. 6,648,640 to Rubbert, et al., the contents of which are incorporated by reference herein.
Other background references related to capturing three dimensional models of dentition and associated craniofacial structures include S. M. Yamany and A. A. Farag, “A System for Human Jaw Modeling Using Intra-Oral Images” in Proc. IEEE Eng. Med. Biol. Soc. (EMBS) Conf, Vol. 20, Hong Kong, October 1998, pp. 563-566; and M. Yamany, A. A. Farag, David Tasman, A. G. Farman, “A 3-D Reconstruction System for the Human Jaw Using a Sequence of Optical Images,” IEEE Transactions on Medical Imaging, Vol. 19, No. 5, May 2000, pp. 538-547. The contents of these references are incorporated by reference herein.
The technical literature further includes a body of literature describing the creation of 3D models of faces from photographs, and computerized facial animation and morphable modeling of faces. See, e.g., Pighin et al., Synthesizing Realistic Facial Expression from Photographs, Computer Graphics Proceedings SIGGRAPH '98, pp. 78-94 (1998); Pighin et al., Realistic Facial Animation Using Image-based 3D Morphing, Technical Report no. UW-CSE-97-01-03, University of Washington (May 9, 1997); and Blantz et al., A Morphable Model for The Synthesis of 3D Faces, Computer Graphics Proceedings SIGGRAPH '99 (August, 1999). The contents of these references are incorporated by reference herein.
The computerized treatment planning has created a vital need for realizing desired tooth displacements and movements, and making tooth position measurements in a consistent, accurate and reproducible manner during virtual orthodontic treatment planning.
Therefore, a novel method and system are disclosed for realizing the desired tooth displacements and rotational movements; and measuring tooth positions in a consistent, accurate and reproducible manner. This is enabled by a novel orthodontic reference coordinate system for calculating tooth displacements and movements in a meaningful manner that obviates the shortcomings of the traditional approach discussed above.